Heterojunction abruptness in gallium arsenide/aluminum gallium arsenide superlattices grown in an atmospheric pressure inverted-vertical MOCVD reactor

A metal-organic chemical vapor deposition (MOCVD) system with an inverted-vertical reactor was built with a fast-switch manifold to minimize pressure variation during switching. Pressure variation is one of the causes of switching transients in the concentration of reactants in the manifold; these transients result in non-abrupt heterojunctions. The purpose of this work was to characterize the manifold and evaluate its effectiveness in controlling pressure variations, and thus the concentration gradient of source materials in the manifold.; The MOCVD growth process, using reactant sources trimethyl gallium (TMG), dimethyl aluminum hydride (DMAH), and arsine (AsH{dollar}sb3{dollar}), was optimized for the growth of gallium arsenide (GaAs), aluminum arsenide (AlAs), and aluminum gallium arsenide (Al{dollar}sb{lcub}rm x{rcub}{dollar}Ga{dollar}sb{lcub}rm 1-x{rcub}{dollar}As). Multiple thin layers (superlattices) of dimensions comparable to those of the transient-induced interfacial layers were grown to characterize the manifold switching transient. Optimum superlattice parameters subject to growth and characterization system constraints were determined. Superlattices were grown on 2 inch Sumitomo semi-insulating GaAs substrates. The structures had a nominal period of 350A, consisting of 125A of GaAs and 225A of Al{dollar}sb{lcub}0.8{rcub}{dollar}Ga{dollar}sb{lcub}0.2{rcub}{dollar}As.; Double crystal rocking curve (DCRC) measurements of three crystal reflections were taken on each specimen. Substrate miscut and superlattice uniformity were determined from (004) plane reflections. Four (115) reflections were measured for each specimen to determine the misorientation of the epitaxial layers with respect to the substrate. The (002) reflections were used to evaluate the periodicity of the superlattice structure itself and to characterize the interfacial layers.; Using DCRC results, a model of the switching transient in the manifold was constructed; bandedge versus thickness and photoluminence (PL) transition energies were predicted from the model. Photoluminescence measurements were performed on the superlattice specimens and on quantum well stacks grown with various growth interruption intervals. The PL results were compared to the model derived from DCRC data and an optimum interval was suggested for the growth interruption required to form abrupt heterojunctions in this system.